Basalt is an igneous mineral ore that can be melted and formed into continuous fibers, staple fibers, e.g., 30 mm in length, micro fibers of, for example, 0.42 μm in diameter, and intermediate lengths and diameters. Basalt fibers have been (a) used to make papermaking fabric, see U.S. Pat. No. 6,926,221; (b) zirconia coated for alkali resistance, see J. Mater. Res., Vol. 9, No. 4, p. 1006 (1996); (c) used for internally reinforcing cement in concrete see U.S. Pat. No. 4,304,604, to reinforce thermosetting resins, particularly epoxy resins and polyester resins, see Popular Plastics, February, 1982, pages 6-8; and (d) formed from a melt of both glass and basalt rock, UK published application 2,019,386 A (1979).
Basalt also has been cut, like granite, to form decorative floor and wall tiles, counter tops, vanities, and the like, and has been smelted at 2,400° C. and cast into tiles for kitchen, baths, churches and cathedrals. Fused basalt powder beads also have been incorporated into thermosetting resins to produce shaped articles, as described in U.S. Pat. No. 6,114,464. Basalt powder also has been mixed with glass powder, ground to a fineness of 1.35 m2/g BET and processed into a foamed glass, as described in U.S. Pat. No. 4,178,163.
Protective armor for heavy but mobile military equipment, such as tanks, high mobility multipurpose wheeled vehicles, e.g., Humvees, aircraft and ships, is known. Such armor usually comprises a thick layer of alloy steel, which is intended to provide protection against heavy and explosive projectiles. Due to its weight, such armor is quite unsuitable for light vehicles such as automobiles, jeeps, light boats, or aircraft, whose performance is compromised by steel panels having a thickness of more than a few millimeters.
Armor for light vehicles is expected to prevent penetration of bullets of any weight, even when impacting at a speed in the range of 700 to 1000 meters per second.
Another consideration in armor design is compactness. A thick armor panel, including air spaces between its various layers, increases the target profile and the wind resistance of the vehicle. In the case of civilian retrofitted armored automobiles which are outfitted with internal armor, there is simply no room for a thick panel in most of the areas requiring protection.
Fairly recent examples of armor systems are described in U.S. Pat. No. 4,836,084, disclosing an armor plate composite including a supporting plate consisting of an open honeycomb structure of aluminum; and U.S. Pat. No. 4,868,040, disclosing an antiballistic composite armor including a shock-absorbing layer. Also of interest is U.S. Pat. No. 4,529,640, disclosing spaced armor including a hexagonal honeycomb core member.
Other armor plate panels are disclosed, e.g., in British Patents 1,081,464; 1,352,418; 2,272,272, and in U.S. Pat. No. 4,061,815 wherein the use of sintered refractory material, as well as the use of ceramic materials, are described.
Ceramic materials are nonmetallic, inorganic solids having a crystalline or glassy structure, and have many useful physical properties, including resistance to heat, abrasion and compression, high rigidity, low weight in comparison with steel, and outstanding chemical stability. Such properties have long drawn the attention of armor designers, and solid ceramic plates, in thicknesses ranging from 3 mm. for personal protection to 50 mm. for heavy military vehicles, are commercially available for such use. Ceramic shields, however, shatter when struck by a fast moving projectile and, therefore, cannot protect against multiple projectiles that strike in close proximity, as occurs with automatic weapons fire.
Much research has been devoted to improving the low tensile and low flexible strength and poor fracture toughness of ceramic materials; however, these remain the major drawbacks to the use of ceramic plates and other large components which can crack and/or shatter in response to the shock of incoming projectiles.
A known form of armor plating using ceramics is produced in Israel by Kibbutz Beit Alpha. It comprises cutting 5 mm steel plates to the sizes required, heat-treating the steel and adding a ceramic coating. One disadvantage of this type of panel is that on completion, the panels are almost impossible to modify. In use, the ceramic coating performs well against the first bullet, but tends to shatter, and thus fails to protect against further projectiles.
Light-weight, flexible armored articles of clothing have also been used for many decades, for personal protection against fire-arm projectiles and projectile splinters. Examples of this type of armor are found in U.S. Pat. No. 4,090,005. Such clothing is certainly valuable against low energy projectiles, such as those fired from a distance of several hundred meters, but fails to protect the wearer against high-velocity projectiles originating at closer range. If made to provide such protection, the weight and/or cost of such clothing discourages its use. A further known problem with such clothing is that even when it succeeds in stopping a projectile, the user may suffer injury due to indentation of the vest to the body, caused by too small a body area being impacted and the inability to absorb the energy of a bullet.
A common problem with prior art ceramic armor concerns damage inflicted on the armor structure by a first projectile, whether stopped or penetrating. Such damage weakens the armor panel, and so allows penetration of a following projectile.
The basalt particle-containing composite articles described herein cause an array of incoming projectiles to pancake or flatten without shattering the articles, while protecting a person or structure without requiring frequent replacement.